Refractory pouring device

ABSTRACT

The invention relates to a refractory pouring device. Such a device is used for teeming of molten metal, in particular in a so-called continuous casting process.

The invention relates to a refractory pouring device. Such a device isused for teeming of molten metal, in particular in a so-calledcontinuous casting process.

Refractory pouring devices of the generic type are known i.a. from EP1133373 B1 and EP 0346378 B1. All of these devices feature a generallytube-like design with a central longitudinal pouring channel.

After assembling of the device, i.e. in its mounted state, the followingapplies: An inlet opening of the pouring channel is arranged at an upperend section of the device, at least one outlet opening is arranged atits lower end section. Molten metal enters the pouring channel/thedevice via said inlet opening and leaves the pouring channel/the devicevia one or more outlet openings.

Said flow of melt is controlled by a so-called stopper rod, acting ontothe inlet opening of the device or a so called slide-valve mechanism.All this is prior art, well known to the skilled person and will not befurther described here.

EP 1590114B1 discloses a pouring device for use in a so-called tubechanging machine.

A basic problem in prior art pouring devices is severe wear/abrasionalong the sliding top surface of the device, thus limiting the servicetime of the corresponding pouring tube/nozzle and increasing the dangerof air ingress because of reduced tightness between the upper surface ofthe pouring device and associated construction elements.

According to EP 0346378B 1 a wear resistant hard refractory material isformed at least around a peripheral edge of the inlet opening.

EP 1133373B1 discloses a pouring device comprising a ceramic tubeelement, supported in a metallic can, in which a ceramic support elementis encapsulated.

Both embodiments are characterized by a multi layer sliding surfacearound the inlet opening.

In other words: Both embodiments are characterized by at least one jointalong the upper sliding surface of the pouring device, said jointdefining the contact zone between different ceramic materials. Differentceramic materials provide different physical properties (like differentthermal expansion) causing further problems to keep the respectivesurface areas of pouring device and adjacent construction elements inintimate contact under heat load.

It is therefore an object of the invention to disclose a possibility toovercome these drawbacks in prior art devices.

The invention is based on the following considerations:

-   -   The partial replacement of the ceramic material around the inlet        opening of the pouring device by a refractory material of        improved wear resistance and temperature stability may increase        the possible overall life-time of the pouring device but may        reduce the service-time of the pouring device in view of        leakages in the system, caused by different thermal expansions        in adjacent areas of the ceramic surfaces.    -   In prior art devices the basic tube element is made of an        alumina-graphite material. Alumina graphite surface are prone to        gouging and finning as a result of a relative softness of the        material. Therefore the upper sliding surface of an embodiment        in accordance with EP 1133373B1 becomes subject to damage during        movement, for example during insertion/ejection from a tube        changer machine. Again the danger of air ingress during casting        may increase.    -   The invention therefore focusses on the requirement of gas        tightness. Highest tightness and insofar prevention of dangerous        air ingress into the system can be achieved best in case of a        large 2-dimensional contact area between the surfaces moved        relative to each other. This requirement may be achieved best by        2 flat/planar sliding surfaces, wherein each sliding surface        features constant physical properties during use. Constant        physical properties may be reached best by surfaces of constant        chemical composition which then necessarily feature constant        physical properties, including the avoidance of any gaps, joints        etc. in the respective surface areas.    -   The arrangement of a one piece refractory layer to provide a        continuous sliding surface could overcome the problems mentioned        but only as part of a corresponding compound system.    -   The idea is to provide the pouring device with a refractory,        monolithic, continuous layer which surrounds the inlet opening        of the pouring channel, thereby providing a continuous sliding        surface, which additionally covers the upper free end of a main        tube element, which further extends downwardly in a cup like        fashion thereby overlapping the outer peripheral surface of the        adjacent end segment of said tube element and which at the same        time provides a collar for the attachment of the pouring device        at corresponding fixation means, such as a tube changer machine.

In its most general embodiment the invention relates to a refractorypouring device featuring a central longitudinal pouring channel with aninlet opening at its first end section and at least one outlet openingat its second end section, comprising:

-   -   a ceramic tube element extending at a distance to the inlet        opening of the pouring channel up to the at least one outlet        opening of the pouring channel,    -   a ceramic envelope, covering the ceramic tube element at least        at its end segment adjacent to the inlet opening of the pouring        channel, in fact    -   all over its outer peripheral surface,    -   all over its annular end face, and    -   all over a transition region in between, wherein    -   the ceramic envelope is a one piece envelope, made of a        monolithic ceramic material and providing an outwardly        protruding collar at the first end section of the pouring        device.

Insofar the pouring device comprises substantially two constructionalelements, the basic tube element and the envelope at its upper endsegment. The envelope not only provides an outer coverage of the upperend segment of the tube element which at the same time defines a collarby which the pouring device may be mounted in a corresponding tubechanging machine but it encapsulates this upper end segment such thatthe upper annular (ring shaped) end face of the tube element is as wellcompletely protected.

Only this part of the envelope now provides the top layer of the pouringdevice and thus the sliding surface at risk.

The inlet opening is now exclusively defined (surrounded) by saidmaterial of said envelope, no joints, seals etc. influencing the wearbehavior of the most endangered refractory part of the device.

Depending on its thickness (in the longitudinal direction of the device)the upper layer of the envelope further defines the upper end of thepouring channel, the lower part of which being defines by the basic tubeelement. Both should be in full alignment with each other to reduce thedanger of wear and clogging.

This amended pouring device differs from known embodiments especially bythe following characteristics:

-   -   the ceramic envelope is a one-piece element covering the more or        less flat upper surface as well as the cylindrical outer surface        of the tube element    -   the ceramic envelope provides the upper sliding surface    -   the upper sliding surface is made completely of a monolithic        ceramic material    -   the material for said envelope may be selected individually    -   the envelope may be cast in one operation cycle    -   an outer metal can may serve as a template during casting    -   the upper sliding surface hat no gaps, joints etc    -   the upper sliding surface may by planar (in a technical sense,        meaning that tolerances in height/thickness/unevenness being <1        mm, especially <0.5 mm, <0.3 mm or <1 mm.    -   the ceramic envelope is imposed onto the ceramic tube element

The general construction of the pouring device may be amended by one ormore of the following features:

The ceramic envelope may be shaped as an inverted cup with a hole in itsbottom, said hole defining the inlet opening of the pouring channel.

The hole may extend in alignment with the pouring channel. In otherwords: The pouring channel has at least 2 sections: an upper sectiondefined by the through opening of the envelope and a lower sectiondefined by the pouring channel of the tube element. In a best mode thesetwo sections are in alignment so as to provide one continuous pouringchannel, the inner surface of which features only one ring shapeddiscontinuity, namely the borderline between the envelope and the tubeelement.

The ceramic tube element can be made of any suitable refractory materialand manufactured by casting, pouring, ramming or pressing, especiallyisostatic pressing. An isostatically pressed/manufactured elementprovides the highest abrasion resistance and life/service time.

The tube element can be made of an alumina/graphite grade, despite itsrelative (mechanical) softness as all its outer surfaces prone togouging and/or finning are now encapsulated by said envelope.

The ceramic envelope is typically a cast element although it may be aswell a preshaped/pre-manufactured workpiece. Casting is performed byusing a suitable/corresponding template, either a lost template or atemplate remaining part of the pouring device. Casting has advantages interms of simplicity of manufacture and reinforcement of the “head area”,i.e. the upper part of the pouring device, which particularly is subjectto thermo mechanical stresses during teeming. In this respect use of aso-called self-flowing or free-flowing monolithic refractory material toprovide the envelope section of the pouring device has severaladvantages, i.e. high density without physical agitation means. Asuitable free-flowing mass is disclosed in EP 525394B1.

The invention includes an embodiment, as illustrated in the attacheddrawing, wherein that part of the ceramic envelope covering the outerperipheral surface of the ceramic tube element is surrounded, at leastpartially, by a metallic can. For sake of clarity: The upper ceramicsurface, the sliding surface, always remains uncovered as well as theinlet opening.

The ceramic material of the envelope may be reinforced by discretemechanical elements, especially by mechanical elements of a differentmaterial, such as refractory or metal fibres, needles etc.

Another reinforcement option is to design such elements as anchors whichare fixed at least at one of the ceramic tube element and the metalliccan. Both variants are illustrated in the attached drawing.

As mentioned above one important advantage of the pouring device is thatsaid part of the ceramic envelope covering the annular end face of theceramic tube element may provide a stepless/seamless gliding surface,arranged at a distance to the annular end face of the ceramic tubeelement. The avoidance of any gaps, joints etc. increases the stability,life/service time of the device while at the same time decreases thepossibility of unwanted air ingress characteristically.

This is best achieved by an embodiment wherein the gliding surface isarranged at a distance to the annular end face of the ceramic tubeelement and perpendicular to the central longitudinal pouring channel orthe central longitudinal axis of the pouring channel/the devicerespectively.

As disclosed above the pouring device may be installed in the bottom ofa metallurgical vessel in a fixed position (fixed i.a. by a mortar) orin a change system like a mechanical so-called tube changer as generallydisclosed in EP 1590114B1.

Insofar the upper end section of the pouring device (that part of theenvelope, surrounding the upper end segment of the tube element) may beconstructed as a collar with either a cylindrical, frustoconical orcubic design. Insofar the corresponding sliding surface may have eitheran outer circular or a rectangular shape, always with said inlet openingwithin its periphery and in most cases in its center.

In this context the invention provides two further alternatives withrespect to the design of the bottom face of the respective collar:

This bottom face(s) may either extend perpendicular to the centrallongitudinal axis of the pouring channel or in an inclined fashion.

When the pouring device is intended to be used in a tube changer devicethe cubic collar area typically provides four bottom faces, serving ascorresponding bearing surfaces for corresponding fixation means such ascompression springs. Further options insofar are disclosed in theaccompanying description of an embodiment.

Typically the pouring channel has a circular cross section at leastalong the first end section of the pouring device.

Embodiments of the invention will now be described with reference to theaccompanying drawing, in which

FIG. 1 is a schematic cross-sectional view of the upper end section of apouring device for use in a tube changer system

FIG. 2 is a schematic cross-sectional view of the upper end section ofthe pouring device according to FIG. 1 perpendicular to the presentationof FIG. 1

FIGS. 3 a,b are cross-sectional views of a complete pouring device and cis a schematic 3-dimensional view of the upper part of this pouringdevice, partly cut-off

The pouring device, illustrated in an orientation according to itsmounted state, features a generally tube like design with a centrallongitudinal pouring channel 30, defining an inlet opening 32 at afirst, upper end section U and two outlet openings 34,36 at a second,lower end section L.

The pouring device comprises a substantially cylindrical tube-element10, made of an alumina-graphite grade (60 m-% Al₂O₃, 30 m-% C, 10 m-%SiO₂) and isostatically pressed, with an increased wall thickness at itsupper free end segment 10 u, defining an upper annular surface 10 s,being arranged in a more or less horizontal orientation. The tubeelement 10 provides a first part 301 (the main part) of the centrallongitudinal pouring channel 30.

Pouring channel 30 has a circular cross section between its inletopening 32 and its outlet openings 34, 36 arranged at a distance tobottom 10 b of tube element 10. As illustrated in the Figures pouringchannel 30 is deflected at its lower end in two opposite directions andboth lines merge into said outlet openings 34, 36 arranged in theceramic wall of tube element 10.

A ceramic envelope 20 covers said tube element 10

-   -   all over the outer peripheral surface 10 p of its upper free end        segment 10 u    -   all over the annular surface 10 s at the upper end of end        segment 10 u    -   all over a transition region 20 t in between        thus giving the envelope 20 a cup shape (pot shape) with its        bottom 20 b on top (inversed cup-shape). Bottom 20 b includes a        central through hole 30 u, defining a second, upper part of        pouring channel 30 and its inlet opening 32.

The total length of the envelope 20 (in the direction of the centrallongitudinal axis A-A of the pouring channel 30) is D, extending fromits free upper surface 20 g downwardly towards outlet openings 34, 36but ending at a distance to said openings 34,36.

The ceramic envelope 20 is a one piece envelope, made of a monolithicrefractory concrete high in alumina, namely: 70 m-% Al₂O₃, 20 m-% SiO₂,1 m-% Fe₂O₃, 4 m-% MgO, 5 m-% other components, all in grain size<1 mm,which becomes free-flowing after addition of about 9 m-% water per 100m-% refractory material.

As may been seen in the Figures envelope 20 has different sizes atdifferent areas. The largest wall thickness is around end segment 10 uof tube element 10, while the cylindrical section extending downwardlyhas the smallest wall thickness. That part of envelope 20 extending ontop of surface 10 s of tube element 10 and providing an upper layer(bottom 20 b) as well as the upper sliding surface 20 g has a thicknessin between.

To improve the adhesion between envelope 20 and tube element 10, theperipheral outer surface 10 p provides female elements such as gaps,depressions etc. into which the material of the envelope may extendduring casting.

In this embodiment upper surface 20 g is flat (planar) to the greatestpossible extent and seamless, as this surface provides a monolithic,continuous gliding surface when installed in a corresponding tubechanger arrangement or mounted to a slide gate mechanism. These mountingand fixation means are not illustrated in detail (as known by theskilled person) but only symbolized by line 40 in FIG. 2.

The outer peripheral area of envelope 20 is covered by a metallic can50, following the varying shape of tube element 10 and envelope 20. Thiscan ends at a distance to sliding surface 20 g (non-visible in FIG. 3c). In other words: sliding surface 20 g protrudes can 50 slightly, inthe embodiment by 2.5 mm.

Anchors (only one of which being illustrated by numeral 60 areprotruding from can 50 to reinforce the cast ceramic material ofenvelope 20.

While tube element 10 is of substantially cylindrical shape envelope 20(and correspondingly can 50) presents different geometric shapes overits length D:

-   -   the upper part, hereinafter referred to as collar C, has a        substantially cubic shape    -   the lower part, hereinafter referred to as pipe section P, has a        substantially cylindrical shape    -   along the intermediate part, hereinafter referred to as        transition region T, the design changes from said cubic to said        cylindrical shape, as best seen in FIG. 3.

Said collar C or its outer metallic can 50 respectively, thus providefour bottom sides CB1, CB2, CB3, CB4 along said transition region T,serving as a bearing surfaces when said pouring device is installed in acorresponding tube changer mechanism in the bottom area of acorresponding metallurgical vessel.

As illustrated in the Figures opposing bottom sides CB1, CB2 extend moreor less perpendicular to the central longitudinal axis A of pouringchannel 30 while bottom sides CB3, CB4 provide an angle a of about 45degrees with respect to said axis A.

Said bottom sides CB3, CB4 may be flat (planar) or curved with respectto central longitudinal axis A. A design with curved bearing surfacescorresponds to that of EP 2269751B1.

In the lower part, specificly above outlet opening 34,36, tube element10 is not covered any more by said envelope 20 and/or can but featuresan external glaze.

The walls of pouring channel 30 including inlet and outlet opening areglazed as well.

1. Refractory pouring device featuring a central longitudinal pouringchannel (30) with an inlet opening (32) at its first end section (U) andat least one outlet opening (34,36) at its second end section (L),comprising: a) a ceramic tube element (10) extending from an area at adistance to the inlet opening (32) of the pouring channel (30) to the atleast one outlet opening (34,36) of the pouring channel (30), b) aceramic envelope (20), covering the ceramic tube element (10) at leastat its end segment (10 u) adjacent to the inlet opening (32) of thepouring channel (30), in fact b1) all over its outer peripheral surface(10 p), b2) all over its annular end face (10 s), and b3) all over atransition region (20 t) in between, wherein c) the ceramic envelope(20) is a one piece envelope, made of a monolithic ceramic material andproviding an outwardly protruding collar (C) at the first end section(U) of the pouring device.
 2. Refractory pouring device according toclaim 1, wherein the ceramic envelope (20) is shaped as an inverted cupwith a hole in its bottom, said hole defining the inlet opening (32) andupper part (30 u) of the pouring channel (30).
 3. Refractory pouringdevice according to claim 2, wherein the upper part (30 u) of thepouring channel (30) extends in alignment with a lower part (301) of thepouring channel (30) defined by said ceramic tube element (10). 4.Refractory pouring device according to claim 1, wherein the ceramic tubeelement (10) is an isostatically pressed element.
 5. Refractory pouringdevice according to claim 1, wherein the ceramic envelope (20) is a castelement.
 6. Refractory pouring device according to claim 1, wherein thatpart of the ceramic envelope (20) covering the outer peripheral surface(10 p) of the ceramic tube element (10) is surrounded, at leastpartially, by a metallic can (50).
 7. Refractory pouring deviceaccording to claim 1, wherein the ceramic envelope (20) is a reinforcedby mechanical elements of a different material.
 8. Refractory pouringdevice according to claim 1 or 6, wherein the ceramic envelope (20) is areinforced by anchors (60) which are fixed at least at one of theceramic tube element (10) or the metallic can (50).
 9. Refractorypouring device according to claim 1, wherein that part (20 b) of theceramic envelope (20) covering the annular end face (10 s) of theceramic tube element (10) provides a stepless gliding surface (20 g),arranged at a distance to the annular end face (10 s) of the ceramictube element (10).
 10. Refractory pouring device according to claim 1,wherein that part (20 b) of the ceramic envelope (20) covering theannular end face (10 s) of the ceramic tube element (10) provides astepless gliding surface (20 g), arranged at a distance to the annularend face (10 s) of the ceramic tube element (10) and perpendicular tothe central longitudinal pouring channel (30).
 11. Refractory pouringdevice according to claim 1, wherein the pouring channel (30) has acircular cross section at least along the first end section (U) of thepouring device.
 12. Refractory pouring device according to claim 1,wherein the ceramic tube element (10) has a larger wall thickness at itsend segment (10 u) surrounded by said ceramic envelope (20) than at itsend segment adjacent to the outlet opening (34,36).
 13. Refractorypouring device according to claim 1, wherein the ceramic envelope (20)has a cubic or cylindrical outer shape in its part (C,T) surrounding theend segment (10 u) of the tube element (10).
 14. Refractory pouringdevice according to claim 1, wherein said collar (C) provides at leastone bottom face (CB1, CB2, CB3, CB4) extending perpendicular to thecentral longitudinal pouring channel (30).
 15. Refractory pouring deviceaccording to claim 1, wherein said collar (C) provides at least onebottom face (CB1, CB2, CB3, CB4) extending at an angle a between 15 and70 degrees relative to a central longitudinal axis (A) of the pouringchannel (30).